The present invention relates to a yarn processing machine for processing and winding an advancing yarn, and more specifically, to a yarn texturing machine of the type disclosed in EP 0 633 213.
The known texturing machine comprises a texturing device and a takeup device. In this machine, a feed system withdraws the yarn from the texturing device and advances it to the takeup device. In the takeup device, the yarn is wound to a package. In particular in machine types with an automatic package doff, time phases occur with a momentary yarn overfeed in the feed system upstream of the takeup device, since the takeup device receives the yarn at a regular speed only during the winding time. As soon as the yarn is removed for purposes of preparing the package doff from a traversing device that reciprocates the yarn in the takeup device, the advancing speed adjusted by the feed system is often greater than the receiving speed of the takeup device. During a package doff, a so-called tie-off bead is wound, after the yarn has been lifted out of the traversing system. Subsequently, the yarn is cut and taken over by a suction device. In this instance, the receiving speed of the takeup device is dependent on the receiving capability of the suction device. In the phases, during which the receiving speed of the takeup device is less than the advancing speed of the feed system, an overfeed of the yarn occurs, which leads to a slack in the yarn between the takeup device and the feed system.
To avoid the formation of laps on the feed system, a yarn accumulator for receiving the slack yarn is used in the known texturing machine. In this connection, the yarn accumulator is arranged in the direction of the advancing yarn directly downstream of the feed system. Consequently, there is a risk that a slack in the yarn, which forms when there is a difference between the advancing speed of the feed system and the receiving speed of the takeup device, propagates to the feed system and leads to the formation of laps due to electrostatic effects.
It is therefore an object of the invention to further develop the texturing machine of the initially described kind such that the slack in the yarn as occurs during a package doff is reliably accumulated. A further object of the invention is to assist the package doff in such a manner that the yarn can be reliably taken over by the suction device during the doffing phase.
The above and other objects and advantages of the present invention are achieved by the provision of a yarn processing apparatus which includes a yarn processing device, such as a texturing device, through which the yarn is advanced. A feed system withdraws the advancing yarn from the processing device and conveys the yarn to a takeup device, and a yarn conveying nozzle is located between the feed system and the takeup device. The yarn conveying nozzle generates an air stream which engages the advancing yarn with a component of movement extending in the direction of the advancing yarn, so that the air stream generates a tension on the yarn upstream of the yarn conveying nozzle and causes an accumulation of slack to be formed in a free space positioned downstream of the yarn conveying nozzle.
The invention is distinct from the apparatus disclosed in DE 22 54 736, wherein a yarn is injected directly upstream of a takeup device into a chamber arranged laterally of the yarn by means of an injection nozzle opposite to the chamber. The relatively strong deflection, that is increased by yarn guides on the lower and upper chamber walls, causes the yarn to be held under tension by the looping friction between the takeup device and the chamber. This effect is contrary to the invention. In the texturing machine of the present invention, a tension is generated on the yarn in its direction of advance. With that, a slack in the yarn toward the takeup device is possible. During the package doff, this slack is desired for purposes of assisting in the transfer of the yarn from the fully wound package to the suction device. This all the more, since greater looping frictions on the yarn could result in that the suction device does not engage the yarn or is unable to hold it. Thus, the invention shows a way of temporarily storing a slack yarn between the feed system and the takeup device without significantly increasing the looping friction and without a risk of lap formation.
Besides the conveying effect, the conveying nozzle is able to lead to a deflection of the slack yarn. In this connection, it has shown that it is favorable to arrange the nozzle bore of the conveying nozzle at an angle less than about 30xc2x0, preferably less than about 20xc2x0.
The conveying nozzle may include a second nozzle bore which is arranged with the first bore to define a plane which intersects or contains the advancing yarn, and to also define an angle which is bisected by the advancing yarn when viewed in a direction perpendicular to the plane. This construction causes a high tension to be generated on the yarn. At the same time, the arrangement of two opposite nozzle bores facilitates a relatively smooth advance of the yarn despite the air stream. In this connection, it is preferred to arrange the nozzle bores relative to each other such that their center axes form an angle less than about 60xc2x0, preferably less than about 40xc2x0, which is bisected by the advancing yarn.
In the production of a textured yarn, the yarn tension in the apparatus of the present invention remains unchanged in the zones upstream of the feed system during the package doff. The yarn delivered by the feed system is withdrawn under tension. This effect is supported in particular by the further development of the invention wherein a rotatably driven conveying roll is positioned in the yarn path upstream of the conveying nozzle, such that the yarn partially loops about its circumference. A conveying roll upstream of the conveying nozzle causes the yarn tension to be increased toward the feed system according to the Eitelwein law (F1=Fo*e:*a). Between the feed system and the conveying roll, no slack occurs in the yarn. The conveying nozzle blows the yarn into the free space. In so doing, the yarn forms, for example, a loop in the air.
Thus, the conveying effect of the conveying nozzle F0 is increased up to the factor e:*a. In this connection, it is advantageous to operate the conveying roll by a turbine drive or an electric drive, so that the circumferential speed is greater than the yarn speed.
With the use of a turbine drive, the conveying roll and conveying nozzle can advantageously be combined into one unit wherein the nozzle bores are formed directly downstream of the point of departure of the yarn from the conveying roll. The turbine drive and the nozzle bore are supplied by a common compressed air supply.
In one embodiment of the conveying nozzle, the yarn is guided in a conveying gap, which is defined by two opposite sidewalls. One of the sidewalls accommodates one or two nozzle bores that terminate in the conveying gap. With that, the air stream is directed to the yarn in a concentrated manner. This construction of the apparatus in accordance with the invention is especially suitable for use inside the traversing triangle in a takeup device. The conveying gap formed transversely of the yarn advance offers the possibility of performing unhindered a transverse movement that is necessitated by the yarn traversing device, when the yarn is wound on a package. The air stream of the conveying nozzle is activated only at the start of the package doff.
To convey the yarn into the free space for receiving the slack, the yarn is guided along the sidewall which opposes the opening of the nozzle bore.
To deflect the yarn at the outlet of the conveying nozzle in a purposeful manner, it is proposed to arrange a guide plate in the extension of the sidewall which opposes the opening of the nozzle bore. The shape of the guide plate permits deflecting the air stream exiting from the conveying gap according to the laws of flow (Coanda effect). Therefore, in particular a guide plate curved in direction toward the free space results in that the air stream exiting from the conveying gap is deflected in a concentrated manner into the free space and leads to the deflection of the yarn.
To receive a yarn, in the event of a great difference between the receiving speed of the takeup device and the advancing speed of the feed system, it is desirable to utilize a bounce plate which defines the free space. In this instance, the slack yarn is accumulated within the free space on the bounce plate in the form of loops and coils. After the package is doffed, and the receiving speed of the takeup device is substantially greater than or equal to the advancing speed of the feed system, the accumulated yarn will be removed.
Since the slack in the yarn occurs only for a very short time during the package doff, the conveying effect of the conveying nozzle is likewise needed only for a short time. To this end, it would be possible to construct the conveying nozzle for movement, so that the yarn comes into the effective range of the nozzle only during a package doff. However, it would also be possible to mount the conveying nozzle stationarily inside the machine. In any event, it is preferred to activate the compressed air supply only during the package doff.